Purification of tetraethyl lead



Patented May 4, 1948 NT C -Q a 7 2,440,810 i l l PURIFICATION OF TETRAETHYL LEAD Alfred Edwin Parmele signor to E. I. du Pont d Wilmington,

No Drawing. Original Serial No.

Wilmington, Del., as-

e Nemours & Company, Del., a corporation of Delaware application May 29, 1943,

489,067. Divided and this application April 12, 1946, Serial No. 661,883

This invention relates to the purification of tetra ethyl lead and more'particularly to the process of removing sludgeforming impurities from the tetra ethyl lead.

In the commercial process of manufacturing tetra ethyl lead and other tetra alkyl lead com- 8 Claims} (01. 260-437) pounds, lead is reacted with sodium to form a lead monosodium alloy. This alloy is then reacted with ethyl chloride or with a mixture of ethyl chlorideand methyl chloride. After the reaction is complete the tetra ethyl lead and other tetra alkyl lead compounds are removed from the reaction mass by steam distillation. Small quantities of finely divided metallic lead and inorganic solids are'carriedover with the tetra alkyl lead in the steam distillation. Such solid suspended materials may beremoved by the method disclosed in my prior Patent No. 1,975,171.

The lead, employed in such process, usually contains small amounts of bismuth and other metallic impurities. Such impurities, especially the bismuth, also reactwith'the ethyl chloride to form organo-metallic compounds which are carried over with the tetra alkyl lead in the steam distillation. These other organo-metallic compounds are less stable than the tetra ethyl lead and tend to decompose and form sludge which Settles in the bottom of tank cars; drums, tanks and the like. This sludge will contain up to about 70% bismuth compounds, up to about 20% lead compounds and small amounts of compounds of other metals. The amount of sludge, obtainable from all of the sludge-forming impurities present in any sample of tetra alkyl lead, is termed the potential sludge content of such sample. g This sludge is objectionable. Frequently, the sludge is highly inflammable andvery reactive on exposure to air. It contains substantial amounts of adsorbed tetra alkyl lead which is always poisonous and hazardous to handle. The sludge, whendeposited in tank cars, drums, tanks, etc., must be periodically removed. The removal and disposal of such sludgeis a hazardous task and requires the use of specially designed equipment and specially trained workers.

The formation of sludge and its removal from tank cars, etc. has long been a problem. -It has been proposedto incorporate, in tetra ethyl lead, compounds for inhibiting the formation of sludge. These sludge inhibitors have not proved to be entirely satisfactory and have not solved the problem. Previously proposed methods of purifying thecrude tetra ethyllead have also failed to solve thisproblem. r f

In a co-pending application Serial No. 393,680 filed May 15, 1941, jointly by William deBenneville Bertolette and myself, now Patent No. 2,409; 383 issued May 14, 1946, it is disclosed that these problems may be very satisfactorily solved by aerating the tetra alkyl lead, whereby the sludgeforming impurities are caused to-form sludge in a small space of time. Such sludge is removed from tetra ethyl lead whereupon the'tetra ethyl lead is purified by the substantially complete removal-of the sludge-forming impurities. While such process is highly successful, it is sometimes desirable to employ other means to remove the sludge-forming materials because of the volatility of the tetra alkyl lead compounds,

It is an object of my invention to overcome the problem of sludge formation in tetra ethyl lead and mixtures containing it. Another object is to provide a method for producing stable tetra ethyl lead compositions. A further object is to provide an improved method of purifying tetra ethyl lead. A still further object is toprovide a simple and improved method for removing sludge-forming compounds from crude tetraethyl lead. Other objects are to provide morestable tetra ethyl lead compositions and to advance the art. Still other objects will appear-hereinafter.

The above and other objects may be accomplished in l accordance with my invention by washing crude steam distilled tetra ethyl lead, containing sludge-forming impurities, with a weak aqueous solution of certain oxidizing agents which will react with the sludge-forming impurities without causing substantial decomposition of the tetra ethyl lead. I have found that some oxidizing agents, when employed in suitable concentration, will react with the sludge forming impurities to convert them to insoluble materials or to Water-soluble materials or both, without causing substantial decomposition of the tetra ethyl lead. I have found further that, by washing crude tetra ethyl lead with such weak aqueous solutions of such oxidizing agents, it is possible to remove the sludge-forming impurities substantially com pletely from crude tetra ethyl lead. The tetra ethyl lead, so treated, is substantially purer and is very much more stable in storage.

Amongst the oxidizing agents, which I have found to be effective for my purpose, are the dichromates of the alkali metals and the alkaline earth 7 metals. The sludge-forming impurities, particularly the bismuth compounds, have been successfully removed from crude commercial tetra ethyl lead by washing the tetra ethyl lead with an equal volume of a 1% aqueous solution of each 3 of sodium dichromate and potassium dichromate. Of these oxidizing agents, I have found the alkali metal dichromates to be the most effective and desirable.

Generally, the Washing of the tetra ethyl lead, in accordance with my invention, is carried out in the presence of air without any attempt being made to exclude air from the washing equipment, or the washing solution. Some oxidizing agents are substantially ineffective when oxygen, as in the air, is excluded from the equipment and from the washing solution. Even when air or other oxygen-containing gas was excluded, by replacing the air with nitrogen, satisfactory removalof the sludge-forming materials, particularly bismuth compounds, was obtained by treatment with solutions of the dichromates of this invention and particularly by the alkali metal dichromates +1% H2804. By +1% HzSOi, I mean that the wash solution contained 1% sulfuric acid.

While all of the oxidizing agents within my invention appear to operate successfully when they are employed in 1% concentration in water, my invention is not to be limited to the use of 1% concentration. Each of the oxidizing agents may be employed in higher-r lower concentration, the exact limits of which will vary with .the individual oxidizing agent. Sodium dichromate and potassium dichromate have been found efiective in concentrations of from 1% to 25% and do not appear .to attack the tetra ethyl lead in any of such concentrations. When the alkali metal dichromates are employed in concentrations as low as 0.5%, the quantity of sludgeforming impurities removed from the tetra ethyl lead falls off rapidly. If it is desired to employ the alkali dichromates with the exclusion of air or oxygen, it is desirable to employ them in slightly acid solution, such as that provided by 1% of sulfuric acid, in order to remove the sludge-forming impurities most efiectively. V

The amount of the aqueous solution to be employed for washing the tetra ethyl lead may be widely varied, it being essential only to employ sufiiciently large amounts to provide suflicient oxidizing agent to react with the sludge-forming impurities, particularly the sludge-forming bismuth compounds, present in the tetra ethyl lead. Generally, about one volume of the solution of the oxidizing agent will be sufficient for washing :5 volumes of tetra ethyl lead and removing the sludge=formingimpurities therefrom. In other words, at least volume of the washing solution should be used for each volume of the tetra ethyl lead; When the oxidizing agent is an alkali metal dichromate, such as sodiumdich-romate and potassium dichromate, it is generally necessary to employ one-half volume of the solution i reach volume of the tetra ethyl .-lead. -I-n prace tice; I have found that the best results are obtainedby employing approximately one volumeeof the aqueous solution of the oxidizing agent for each volume of the tetra ethyl lead. Much larger volumes-of the washing solution can be employed, but without advantage. Attack of the tetra ethyl lead andqof the sludge-forming impurities by the oxidizing agent depends upon the particular oxidizing agent employed and its concentration in the aqueous solution, rather than the amount of aqueous solution employed. 7

, iln carrying out the washing of the crude tetra ethyl lead in accordance with my inventiomthe tetra ethyl lead and the aqueous solution-are pl c in a t l c nt ner p ovi ed w th meansf-or agitation. The tetraethyl lead and --operations, where contact between the two materials is less easily accomplished, one to two hours agitation may be necessary. When the reaction of the oxidizing agent with the sludge-forming materials is complete, the agitation is stopped and the mixture allowed to settle whereupon 2 layers are formed, the lower layer being the purified tetra ethyl leadand the upper layer being the aqueous solution. When the sludge-forming impurities are converted to insoluble materials, 7

, they will collect in the aqueous layer mainly at the interface between the two layers. The purified tetra. ethyl lead may be drawn on? from beneath the water layer, While it is not always necessary to filter the purified tetra ethyl lead, it is generally desirable to filter it so as to insure that no preci itated material yvillbe included in the purified tetra ethyllead. 7

'It will be understood that the oxidizing agents specifically named are given for illustrative purposes and that various modifications and variations may be made therein without departing .from the spirit or scope .of my invention. On the other hand, I intend to claim ,my invention broadly as in :the appended 'claims. While I have disclosed the mixing of the tetra .ethyl lead with the desired volume of. the aqueous solution ina single operation, and that is the preferred th d of practicin my inve tio it will b pp n th the -tetr ethyl ead an b s jected to successive washings with smaller increm nts oi the washing solution, Also,,,-the washing solution may contain trisodium phosphate orother wettinga ent disclose In my hat- .en-t No. .1,9!7-5,1?71 so as to-at the same ti-me remove finely divided metallic lead and the like f-re n the tetra th l lead and combine the pro ess o t i te o th he process o such pate t. The use of such wettin a ent will aid di pe sin slnde e orming impurities, which have be n conve t d o insoluble inaterialstin t e aqueous solution and aid in the removal of such matierials fromthetetraethylilead- When thecxidi ing agent emplo ed :is an al a met eliminate, the "washin so ution maycont 11 about one to about 2% oia salt suchas soda-.1; chloride and sodium acetate to improve the filtering qualities of the precipitated impuritics and to ove ome the tendency toward t iformati n of an emulsion betwe n thet tra ethyl leadiand th admonssolution.

Earthen the activ ty of X a th d chromates, usually i ins a ents, such be improved by lovin -a small propor on offence-oxidizin 4 mine al acid, snchabout 1% o sul uric a id hydrochloric ac. the aqneonsisolution.

The washin of to. re ethyl leadwith the aqueous solutions of .oxidizing agents in accordance with my invention imay'alsp be emnleyed'zin-combinati n w th .he aeration process d sclosed in Batent flo. ;.2.4co.3s.3.. such -,c se, the..=oxi.diz- .in .agents will assist intheioxid t on of the lndgeetormingcimpurities :bythe ai the oxidi n a ents are .employediin crrlow conc nt ations at which th y-themselves are ineirect ve t remove the isludse formins impurities. Under such conditionsgtheoxittizing agents even when appear to act as catalysts in the aeration process.

This application is a division of my copending application Serial No. 489,067, filed May 29, 1943, now Patent No. 2,410,356, issued October 29, 1946.

I claim:

1. The method of purifying steam distilled tetra ethyl lead, containing sludge-forming impurities, which comprises agitating the tetra ethyl lead with at least volume of a weak aqueous solution of an oxidizing agent of the class consisting of the alkali metal dichromates and the alkaline earth metal dichromates for sufficient time for the oxidizing agent to react with the sludge-forming impurities, the concentration of the oxidizing agent in the aqueous solution being from about 1% to about 25%, settling the mixture and separating the tetra ethyl lead from the aqueous solution and the reaction products of the oxidizing agent with the sludge-forming impurities.

2. The method of purifying steam distilled tetra ethyl lead, containing sludge-forming impurities, which comprises agitating the tetra ethyl lead with approximately 1 volume of a weak aqueous solution of an oxidizing agent of the class consisting of the alkali metal dichromates and the alkaline earth metal dichromates for sufiicient time for the oxidizing agent to react with the sludge-forming impurities, the concentration of the oxidizing agent in the aqueous solution being from about 1% to about 25%, settling the mixture and separating the tetra ethyl lead from the aqueous solution and the reaction products of the oxidizing agent with the sludge-forming impurities.

3. The method of purifying steam distilled tetra ethyl lead, containing sludge-forming impurities, which comprises agitating the tetra ethyl lead with approximately 1 volume of a weak aqueous solution of an oxidizing agent of the class consisting of the alkali metal dichromates and the alkaline earth metal dichromates for sufiicient time for the oxidizing agent to react with the sludge-forming impurities, the concentration of the oxidizing agent in the aqueous solution being approximately 1%, settling the mixture and separating the tetra ethyl lead from the aqueous solution and the reaction products of the oxidizing agent with the sludge-forming impurities.

4. The method of purifying steam distilled tetra ethyl lead, containing sludge-forming impurities, which comprises washing the tetra ethyl lead with at least /z volume of an aqueous solu- 6 tion of an alkali metal dichromate containing from about 1% to about 25% of alkali metal dichromate.

5. The method of purifying steam distilled tetra ethyl lead, containing sludge-forming impurities, which comprises washing the tetra ethyl lead with approximately 1 volume of an aqueous solution of an alkali metal dichromate containing from about 1% to about 25% of alkali metal dichromate.

6. The method of purifying steam distilled tetra ethyl lead, containing sludge-forming impurities, which comprises washing the tetra ethyl lead with approximately 1 volume of an aqueous solution of an alkali metal dichromate containing about 1% of alkali metal dichromate.

7. The method of purifying steam distilled tetra ethyl lead, containing sludge-forming impurities, which comprises agitating the tetra ethyl lead with approximately 1 volume of a weak aqueous solution of a non-oxidizing mineral acid and an oxidizing agent of the class consisting of the alkali metal dichromates and the alkaline earth metal dichromates for sufficient time for the oxidizing agent to react with the sludge-forming impurities, the concentration of the oxidizing agent in the aqueous solution being from about 1% to about 25%, settling the mixture and separating the tetra ethyl lead from the aqueous solution and the reaction products of the oxidizing agent with the sludge-forming impurities.

8. The method of purifying steam distilled tetra ethyl lead, containing sludge-forming impurities, which comprises washing the tetra ethyl lead with approximately 1 volume of a slightly acidified aqueous solution of an alkali metal dichromate, containing about 1 of an alkali metal dichromate and about 1% of a non-oxidizing mineral acid.

ALFRED EDWIN PARMELEE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,645,375 Daudt et al. Oct. 11, 1927 1,975,171 Parmelee Oct. 2, 1934 2,004,160 Downing et a1. June 11, 1935 2,038,703 Bake et a1 Apr. 28, 1936 2,293,214 Peck Aug. 18, 1942 2,400,383 Bertolette et a1 May 14, 1946 

